The present invention relates generally to antennas, and in particular, to slot spiral, miniature antennas.
Spiral antennas are well known in the art as means of providing circularly polarized radiation over a broad frequency band. The most popular configurations are the dual arm equiangular. Archimedean and logarithmic spirals, in which the two arms are fed in antiphase at the center (see, for example, U.S. Pat. Nos. 3,781,898 and 3,969,732 both) to Holloway). The lowest frequency of operation in such antennas is determined by the diameter of the spiral, where the outer circumference is equal to the longest wavelength.
There are many applications in which the small size of the antennas is a desirable feature due to cosmetic, security, aerodynamic and other reasons. There are also applications in which surface conformability of the antennas or a possibility to mount an antenna on a platform, which is not flat or planar, is a desirable feature.
For example, in mobile devices (e.g., cellular phones, PDAs, laptops, etc), reducing antenna""s size is required since the amount of space available for mounting an antenna is limited. For antennas mounted on airplanes, the protrusion of the antenna beyond the surface of the plane should be minimized in order to reduce the effect of the antenna on its aerodynamic properties.
Generally, a decrease in the size of the spiral antenna may be accomplished by the reduction of its aperture and/or thickness.
Various approaches are known in the art for gaining an aperture reduction of the antennas. For instance, the aperture reduction may be achieved by utilization of perimeter squared spiral configurations. Further aperture reduction may also be accomplished by utilizing a square spiral with a zigzag track to produce a slow wave structure (see, for example, U.S. Pat. No. 3,465,346 to Patterson and xe2x80x9cReduced size spiral antennaxe2x80x9d, Proc. 9-th European Microwave Conf., September. 1979, pages 181-185, by Morgan).
The slow-wave structure features a slower phase velocity and, consequently, a smaller radiation zone at the lowest operating frequency that, in turn, allows the diameter of the slow-wave antenna to be reduced significantly. The reduction in size is proportional to the degree of slowing of the slow-wave, as measured by the slow-wave factor, which is defined as the ratio of the phase a velocity of the propagating wave in the traveling wave structure to the speed of light in a vacuum.
Various approaches for aperture reduction were implemented by implementation of multi-arms antennas. For example, U.S. Pat. No. 6,023,250 to Cronyn discloses an antenna having a plurality of exponential-spiral shaped antenna arms in which each of the arms includes an antenna clement having a sinuous portion.
Since a spiral in the antennas radiates bidirectionally, backed metallic and absorbing cavities are generally used (see, for example, Morgan, xe2x80x9cReduced size spiral antennaxe2x80x9d, Proc. 9-th European Microwave Conf., September. 1979, pages 181-185). The backed cavity is employed to redirect half of the energy constructively to form a main beam. Theoretically, the optimum cavity depth is a quarter of the wavelength xcex. If the frequency approaches the value xcex/2, then the reflected energy is in antiphase with the forward radiation, that results in beam splitting and a degraded match. Therefore, many conventional spiral antennas employ absorbing cavities that absorb the energy within the cavity, thereby preventing it from reflecting destructively and providing broadband operation. Despite the technical advantages, adding a cavity to the spiral antenna may significantly increase its thickness to the overall antenna structure, that contradicts the small size requirements.
A slot spiral antenna with an integrated planar balun and feed is described in U.S. Pat. No. 5,815,122 to Numberger, et al. The slot spiral antenna is produced by using standard printed circuit techniques. A conducting layer of the material substrate is etched to form a radiating spiral slot. The balun structure includes a microstrip line that winds toward the center of the slot spiral. At the center of the slot spiral, the feed is executed by breaking the ground plane of the microstrip line with the spiral slot. The technique disclosed in U.S. Pat. No. 5,815,122 substantially reduces the size of the conventional spiral antennas, such that the antenna may be suitable for incorporating into the skin of some mobile devisees. However, the diameter of this antenna is still big in order to fit the external surface of a mobile phone.
Thus, there is still a need for further improvement in order to provide an antenna that might include the broad band performance, surface conformability, uni-directionality and reduced aperture and thickness (e.g.. suitable for flush mounting with the external surface of a mobile phone), all the features in a single package.
The present invention satisfies the aforementioned need by providing a slot spiral antenna that is geometrically smaller than another antenna performing the same functions.
The antenna includes a conductive layer formed on a first side of a dielectric substrate. A slot arranged along a spiral curve is formed in the conductive layer by using conventional printed circuit techniques. A slotline of the slot has a slow-wave structure, e.g. zigzag, meander line, sine, fractal, etc.
The antenna also includes a planar balun formed on a second side of the substrate. The balun is in the form of a conductive layer strip positioned beneath a section on the conductive layer defined by an area between two neighboring parts of the slotline. The conductive layer strip bas a shape that replicates a pattern of the two neighboring parts of the slotline. For example, when a slotline of the slot has a zigzag shape, the shape of the conductive layer strip may resemble a sine pattern.
The conductive layer strip provides a balanced feed to the slot at a feedpoint that is defined by a place wherein a projection of said conductive layer strip on the second side intercepts the slotline. Electromagnetic coupling between the conductive layer strip and the slotline without electrical contact causes the exciting of the slotline.
In order to limit the radiation to one direction, a thin cavity may be included. The cavity may face either the first or second side of the substrate. The cavity may be filled with high dielectric loss material, low dielectric loss material or a combination thereof.
If it is necessary to decrease the coupling between the slotline and the conductive layer strip, then the antenna may include vias made near singularity points of the slow wave structure, e.g., near zigzag vertexes.
According to one embodiment of the present invention, in vertexes of the zigzag, an angle of the teeth may have a magnitude of about zero degrees.
The antenna of the present invention is geometrically smaller than another antenna performing the same functions, but without such features as the slow-wave structure of the slotline and the replication of a pattern of the slotline shape by a conductive layer strip.
The antenna of the present invention has many of the advantages of the prior art techniques, while simultaneously overcoming some of the disadvantages normally associated therewith.
The antenna according to the present invention may be mounted flush with the surface of a mounting platform.
The antenna according to the present invention may be relatively thin in order to be inset in the skin of a mounting platform without creating a deep cavity therein.
The antenna according to the present invention may be readily conformed to complexly shaped surfaces and contours of a mounting platform.
The antenna according to the present invention may be easily and efficiently manufactured.
The antenna according to the present invention is of durable and reliable construction.
The antenna according to the present invention may have a low manufacturing cost.
In summary, according to one broad aspect of the present invention, there is provided a slot spiral antenna comprising:
a dielectric substrate of a predetermined form having a first surface and a second surface,
a conductive layer on said first side of the substrate said conductive layer including at least one slot defined by a slotline arranged in the form of a spiral curve, at least a portion of the slotline having a pattern corresponding to a slow-wave structure;
a planar balun formed on said second side of the substrate, the balun being a conductive layer strip positioned beneath a section on the conductive layer defined by an area between two neighboring parts of the slotline, each neighboring part having a pattern; said conductive layer strip having a shape substantially replicating the pattern of said two neighboring parts of the slotline, said conductive layer strip configured to provide a balanced feed to said at least one slot at a feedpoint defined by a place wherein a projection of said conductive layer strip on said second side intercepts the slotline, thereby exciting the slotline by causing electromagnetic coupling between said conductive layer strip and slotline without electrical contact.
According to another broad aspect of the present invention there is provided a a slot spiral antenna comprising:
a dielectric substrate of a predetermined form having a first surface and a second surface,
a conductive layer on said first side of the substrate, said conductive layer including at least one slot defined by a slotline arranged in the form of a spiral curve, at least a portion of the slotline having a pattern corresponding to a slow-wave structure;
a planar balun formed on said second side of the substrate, the balun being a conductive layer strip positioned beneath a section on the conductive layer defined by an area between two neighboring parts of the slotline, each neighboring part having a pattern; said conductive layer strip having a shape substantially replicating the pattern of said two neighboring parts of the slotline, said conductive layer strip configured to provide a balanced feed to said at least one slot at a feedpoint defined by a place wherein a projection of said conductive layer strip on said second side intercepts the slotline, thereby exciting the slotline by causing electromagnetic coupling between said conductive layer strip and slotline without electrical contact,
wherein said antenna being fitted for use in a hand-held communication device.
According to yet another broad aspect of the present invention, there is provided a slot spiral antenna comprising:
a dielectric substrate of a predetermined form having a first surface and a second surface,
a conductive layer on said fast side of the substrate, said conductive layer including at least one slot defined by a slotline arranged in the forms of a spiral curve, at least a portion of the slotline having a pattern corresponding to a slow-wave structure;
a planar balun formed on said second side of the substrate, the balun being a conductive layer strip positioned beneath a section on the conductive layer defined by an area between two neighboring parts of the slotline, each neighboring part having a pattern; said conductive layer strip having a shape substantially replicating the pattern of said two neighboring parts of the slotline, said conductive layer strip configured to provide a balanced feed to said at least one slot at a feedpoint defined by a place wherein a projection of said conductive layer strip on said second side intercepts the slotline, thereby exciting the slotline by causing electromagnetic coupling between said conductive layer strip and slotline without electrical contact,
wherein said antenna being automatically configured to operate over at least one octave frequency band.
According to still another broad aspect of the present invention, there is provided a hand-held communication device comprising an antenna comprising:
a dielectric substrate of a predetermined form having a first surface and a second surface,
a conductive layer on said first side of the substrate, said conductive layer including at least one slot defined by a slotline arranged in the form of a spiral curve, at least a portion of the slotline having a pattern corresponding to a slow-wave structure;
a planar balun formed on said second side of the substrate, the balun being a conductive layer strip positioned beneath a section on the conductive layer defined by an area between two neighboring parts of the slotline, each neighboring part having a pattern; said conductive layer strip having a shape substantially replicating the pattern of said two neighboring parts of the slotline, said conductive layer strip configured to provide a balanced feed to said at least one slot at a feedpoint defined by a place wherein a projection of said conductive layer strip on said second side intercepts the slotline, thereby exciting the slotline by causing electromagnetic coupling between said conductive layer strip and slotline without electrical contact.
According to yet another broad aspect of the present invention, there is provided a hand-held communication device comprising a slot spiral antenna including a balun, wherein the antenna is adapted to provide a mutual operation of least three communication services operating in non-overlapping frequency bands.
According to yet another broad aspect of the present invention, there is provided a hand-held communication device comprising a slot spiral antenna including a balun, wherein said antenna being automatically configured to operate over at least one octave frequency band within the frequency range of about 800 MHz to 3 GHz.
According to yet another broad aspect of the present invention, there is provided a method for fabricating a slot spiral antenna comprising:
providing a dielectric substrate of a predetermined form having a first surface and a second surface;
forming a conductive layer on said first side of the substrate, said conductive layer including at least one slot defined by a slotline arranged in the form of a spiral curve, at least a portion of the slotline having a pattern corresponding to a slow-wave structure;
forming a planar balun on said second side of the substrate, the balun being a conductive layer strip positioned beneath a section on the conductive layer defined by an area between two neighboring parts of the slotline, each neighboring part having a pattern; said conductive layer strip having a shape substantially replicating the pattern of said two neighboring parts of the slotline, said conductive layer strip configured to provide a balanced feed to said at least one slot at a feedpoint defined by a place wherein a projection of said conductive layer strip on said second side intercepts the slotline, thereby exciting the slotline by causing electromagnetic coupling between said conductive layer strip and slotline without electrical contact.
According to still another broad aspect of the present invention, there is provided a conductive layer antenna comprising a dielectric substrate of a predetermined form having a microstrip on one side of the substrate arranged in the form of a spiral curve, at least a portion of the microstrip having a pattern of zigzag; the zigzag having a reversed S-type shape.
There has thus been outlined, rather broadly, the more important features of the invention so that the detailed description thereof that follows hereinafter may be better understood, and the present contribution to the art may be better appreciated. Additional details and advantages of the invention will be set fort in the detailed description.